Ventilation Factors We Cannot Control – Part 4 Taking It To The Streets by PJ Norwood

This multi-part blog series has focused on the ventilation issues that occur on our fireground and their impact on the tactical assignments. We have discussed when doors and windows fail and the devastating impact a failure can have on companies operating inside that environment.

In this last part, I want to discuss the officer’s role in predicting these events that will help keep their members safe. However, it must be stated this is not just the officer’s role. Every member has the role of size up and to constantly evaluate the conditions. Everyone on the fireground should be completing an initial and on going size up for their self. This size up will have a different focus based on the tactical assignments of the company or member. The evaluation of the fire behavior and predicting rapid-fire events is everyone’s responsibility and must be included in your size up.

Today, firefighters are routinely set up for failure. We train in class A burn buildings using hay and pallets as the fuel package. This fuel reacts very different then the fuel packages we see on the fireground. In a class A burn building when we vent, everything gets better. On the fireground when we vent it only gets better with a coordinated fire attack. We also train our members by bring our firefighters into a flashover simulator, which is an important educational tool. This tool helps us educate firefighters to the warning signs of a flashover, which is critical. However, many instructors have their firefighters leaving these training sessions thinking they witnessed a flashover when in fact they are witnessing a rollover or flameover event. Flashover and flameover are two very different events. Granted each one can kill firefighters but we must begin to truly educate our firefighters in fire behavior and stop blurring the lines.

Take a look at National Institute for Occupational Safety and Health (NIOSH) Line of duty death report, which does a good job indicating that a flameover impacted Firefighter Solomon from Atlanta Fire-Rescue on November 23, 2006.

We are all aware the fire environment has changed which has impacted our fires. This change highlights the necessity to begin evaluating our fireground differently then we have always done in the past.

We cannot continue to base our decision-making process solely on training and experiences that were not taught to evaluate today’s fires.

Many US firefighters feel we cannot learn anything from our European brothers and sisters. However, the Europeans have a model that we can learn from. They are taught to recognize the “signs and symptoms” of flashover and backdraft in response to changing fuel loads. A focus on compartment fire behavior training was revolutionizing their approach to fire attack and tactical ventilation. There are differences between the European fire service and ours and I and not suggesting we should mimic everything they do. I also am not trying to introduce you another acronym. My goal is to provide you with a different perspective of evaluating the dynamic event in front of you.

The Europeans look at five items in their evaluation of the fireground to help predict extreme fire behavior. The European model looks at and focus’s the incident commander attention to look at five components. Those components are the Building, Smoke, Air Track, Heat, and the Flames.

The four fire behavior indicators, smoke, air track, heat and flame can be used to rapidly assess the stage of fire development and the changes that are likely to occur before, during and after intervention.

Lets break down this model and apply it to our fireground

The Building

Unlike the other fire behavior factors, the building and its contents are present prior to ignition and can be examined during your pre-fire plan. A failure in this process is we do not preplan many, of our private dwellings. Knowing our districts and making every opportunity to learn about the features and contents of dwellings in your district is critical.

During unofficial preplans, (EMS calls or other non-fire events) visits during construction or “open houses” the real estate brokers hold regularly gives us opportunities to get in and see what is occurring in your districts. We need to start to focusing on the interior linings and contents of the structure and learning how those linings affect the fire behavior. We must have an understanding how the interior properties will absorb or radiate heat back into the room. Understanding how materials will burn and their heat release rates will help you understand how rapidly a fire will become ventilation limited. Knowing what type of insulation lies in the walls and ceilings and how “tight” the building is will also help you understand how the fire will react.

The construction industry in changing with a goal of efficiency and we must keep up with what’s going in our districts. The building industry primary focus is keeping the cold out and the heat in during the winter months and the heat out and the cold in during the summer months.

In a well-insulated building or room, the temperatures will rise more rapidly than a room with linings that have poor insulation properties. This can slow the fires growth rate. However, these materials will hold the absorbed heat energy for a long period of time while it waits for the additional properties it needs to continue its rapid development, oxygen.

Doors and windows will also fail complicating the issue. Refer back to part one and part two of this blog series regarding window and door failure

Smoke conditions and the pattern of smoke and air movement are two of the critical indicators of fire behavior. The location, appearance and how it is moving provides valuable information related to the location of the fire, its stage of burning (fuel or ventilation controlled) and the stage of the fire in different areas of the building.

At all fire incidents all members must begin their assessment of smoke and air track indicators. This assessment is just like all other parts of your size up. They must be done as soon as possible and must be continually assessed during the entire incident

Some of the visual items that must be evaluated to define smoke and air track are as follows:

Height of Neutral Plane - As the fire develops, the neutral plane (the boundary between the heated smoke and the cooler air) will lower, and the thickness of the smoke gases will increase.

A high neutral plane could indicate that the fire is in the early stages of development.

A very low neutral plane could indicate very rich backdraft conditions.

A sudden rise could indicate that ventilation has occurred.

Gradual lowering often indicates a build-up in fire gases and progress to flashover.

Sudden lowering could indicate a rapid intensification of the fire.

Volume, Location and Color – The visible smoke, color, volume and location is not always a reliable indicator of the location, size, stage of development or materials burning. Heated smoke will rise vertically and spread out horizontally when vertical movement is restricted. Smoke can travel through concealed voids and shafts and emerge in totally unexpected locations. As with all fire indicators, it is very important not to rely just one indicator.

Buoyancy & Pressure - Smoke seen rapidly expanding upward and rolling indicates that the gases are at a high temperature. In contrast, smoke that’s released with lower temperatures has a tendency to slowly drift upward or even downward. Lower buoyancy could indicate relatively low compartment temperatures, or it could be caused by cooling that has occurred as the smoke has travelled through uninvolved sections of the structure. Smoke forced out under pressure usually indicates that the exit point is close to the fire source.

Air Track - The air track is the flow of air toward the base of the fire and the movement of the heated combustion products up and out of the compartment.

Velocity & Direction When an opening is created in a fire compartment, the heated gases will flow out the top of the opening, and cool air will flow in through the bottom of the opening. A total and sudden inward movement of the air track could indicate a potential backdraft event. In some cases, there will be an out rush or smoke, the backdraft will follow this.

Smoke or flame being discharged from the entire height of ventilation openings usually indicates that it’s an outlet and that the ventilation inlet is in another part of the structure. An opening that is both a ventilation inlet and outlet will show signs of smooth or turbulent flow at the air/smoke interface.

Flow—Turbulent or Smooth When viewing an opening in the fire compartment, a slow and laminar air/smoke interface could indicate that the fire is in the early stages and most likely fuel-controlled. If the air track is fast and turbulent, this could indicate a working fire that is in the ventilation-controlled phase.

Heat

While heat cannot be observed directly, observation of the effect of heat on air track (i.e., velocity of smoke discharge), the building or exposures, and changes in temperature can be significant fire behavior indicators. It is important to remember that our personal protective equipment provides significant insulation and slows the transfer of heat and resulting sensation of changes in temperature. Making it more difficult to discern the changes in temperature.

Blackening of Windows with no Flame Showing - Blackening indicates rich conditions and is often accompanied by oily deposits on the inside of windows. This indicator may be difficult to see on double- or triple-glazed windows.

Cracking or Crazing of Glass – Rapid heat build-up can result in cracking of glass, and crazing which is a network of fine cracks that can be seen when the heat build-up has been slower.

Blistering or Discoloration of Paintwork -This can be easily seen on lightweight internal doors, but may be absent in heavy, well-insulated exterior doors. The evaporation of a water film applied across a door surface may help to indicate the presence of the heat layer. This will occur at temperatures as low as 212 degrees F (100 degrees C).

Sudden Heat Build-Up - This indicator is frequently noted as a sign that flashover or backdraft is imminent. However, firefighters should NOT rely on this indicator, as it often occurs AFTER some form of fire gas ignition has commenced in the upper section of the compartment. This is often obscured from view, and by the time firefighters feel the heat through their PPE, they will be in a very dangerous situation.

Flame- Which are burning gases are the most obvious or visible indicator observed by firefighters. Firefighters are, at times, like moths to the flame. When we see flames we will instinctually focus on the flaming combustion. However, do not become so focused on the visible flames, it may cause you to miss more important, but subtle building, smoke, air track, and heat indicators. Also remember there are two ways to reduce the burning gasses. We can do that by applying water or limiting the air.

We have been told that the color of the flame indicates the products burning. Today this is an unreliable indicator. Our residential building is filled with multiple types of fuels making the assessment of color in relation to products burning difficult.

While I am not trying to inundate you with another acronym or tell you that you have been doing is wrong. What I am saying is we must change and adapt our ways to keep up with the changes that have and continue to change around us. Just because your fires have gone out does not mean you are managing or performing the most optimal way. I am also not saying there is one way for every incident.

As smart educated firefighters and officers we must analyze what we have, what is occurring and what will be occurring. We must then match the current resources to the incident while constantly monitoring the complete fireground including the fire behavior. We must be prepared for uncontrolled ventilation and signs of rapid-fire development some caused by firefighters on the scene and many other are factors we cannot control.

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